The use of mildly acidic solutions containing active chlorine, mostly in the form of hypochlorous acid, is known in various disinfection processes pertaining to several industrial fields including healthcare and sanitary applications; in food industry for instance, this kind of solutions are employed for the elimination of pathogenic bacteria such as Salmonella or Escherichia coli from the manufacturing cycle of foods of various kinds. The continuous production of solutions containing free active chlorine at appropriate concentration (e.g. 50-100 ppm) may be carried out electrolytically in unseparated or in two-compartment cells, i.e. in cells partitioned by a semipermeable diaphragm or cation-exchange membrane and fed with alkali chloride brine; in the latter case, the desired solution is generated in the anodic compartment, while at the corresponding cathodic compartment an alkaline solution with good cleansing properties is obtained. In such systems, however, the salinity of the resulting anodic product is too high to be suitable for use in many of the typical fields of application (food industry, hospitals, agriculture). An anodic product of superior quality can be obtained with an electrolytic cell equipped with three compartments, with a circulation of concentrated brine in an intermediate compartment, separated from the cathodic compartment by a cation-exchange membrane and from the anodic compartment by an anion-exchange membrane. The above selection of separators allows the selective migration of sodium ions to the cathodic compartment, where a diluted alkali solution is generated (e.g. 50-100 ppm of caustic soda when the brine consists of sodium chloride) and of chloride ions to the anodic compartment, where chlorine is generated. None of the commercially available anionic membranes, however, is capable of resisting the attack of chlorine-containing acidic solutions for more than a few tens of hours, despite their alleged resistance to oxidants; maintenance costs for the replacement of anionic membranes in three-compartment cells have hence proven not well suited to the needs of industry.
It was thus identified the need to provide an electrolytic cell for the production of acidic solutions containing active chlorine overcoming the drawbacks of the prior art, especially in terms of durability of the components.